As light sources of a lighting device and a display device, semiconductor laser elements have been used as the light sources in place of a lamp. With use of a plurality of semiconductor laser elements, an optical output larger than that of a lamp can be obtained, and a wider color reproduction range and a longer life of a light source can also be achieved. Note that, it is known that the semiconductor laser elements have high dependency upon temperature, and maintain a larger output and a longer life as the temperature is lower. Therefore, a Peltier element, a water-cooling cooling mechanism, and the like are proposed as cooling means for the semiconductor laser elements (Patent Document 1). However, as means of compensating for the temperature dependency of the semiconductor laser elements, compensation means of using an optical output automatic control (or automatic power control: hereinafter abbreviated as “APC”) circuit for controlling an optical output by making an adjustment to an input electric current, not to the temperature, is generally adopted (Patent Document 2).